Green Mountain Reservoir, one of the biggest reservoirs in Summit County, is low this summer, but it’s not as low as in previous drought years.

The reservoir is currently storing about 101,000 acre-feet of water — 32.9 billion gallons — James Heath, division engineer for the Colorado Division of Water Resources, said in an email. He noted that the reservoir is typically nearly full around this time of year. A full Green Mountain Reservoir is about 154,000 acre-feet of water, or approximately 50 billion gallons.

However, Heath said in previous drought years like 2002 and 2012, there was less water stored in the reservoir than there is this year.

Heath explained that the runoff from the Blue River this year was not enough to fill both Dillon Reservoir, which is upstream, and Green Mountain Reservoir, which is downstream.

“Dillon Reservoir was able to physically fill, while Green Mountain Reservoir did not,” Heath said. “However, Green Mountain Reservoir did achieve a legal fill, and Denver Water and Colorado Springs Utilities will be making releases primarily from Wolford Mountain Reservoir and Williams Fork Reservoir to replace the water.”

Releases from Green Mountain Reservoir make their way to the Colorado River to appease those downstream with senior water rights. Heath said these releases replace upstream depletions from West Slope diversions and the Colorado Big Thompson project, which delivers the approximate volume of Dillon Reservoir to the South Platte Basin.

Heath noted that there has been a call for irrigation water rights downstream in the Grand Valley, which means senior water users have requested to restrict the use of water among junior water users because there is not enough water in the system to allow all water diversions. This requires Green Mountain Reservoir to stop storing, pass inflows and make releases.

While calls on Green Mountain Reservoir can restrict use for junior water users, there is a group of western Colorado water users that have historically benefited from releases out of Green Mountain Reservoir, called historic user pool beneficiaries, that are allowed to continue to divert after a call is placed on the river.

Since July 10, the reservoir water level has dropped about 7,000 acre-feet, or 2.2 billion gallons, according to the Colorado Division of Water Resources website. For most of July, Green Mountain Reservoir’s discharge to the Blue River was below the historic average.